1. Field of the Invention
This invention concerns an assembly for molding an ocular lens blank which is later lathed to make an intraocular lens or a contact lens.
2. Description of the Related Art
Many types of ocular lenses are sold by manufacturers to retailers, opticians, optometrists and ophthalmologists as a finished product that is ready to wear. In some circumstances, however, lens blanks are purchased from the manufacturer and then lathed and finished to make a lens having a desired prescription. Lens blanks are particularly useful for making lenses having unusual prescriptions that might be difficult to obtain directly from the manufacturer.
Lens blanks are often cut into the shape of a thick button from rod stock or sheet stock. The blank is mounted in a collet and one side is lathed, often by initially using a roughing lathe before a finishing lathe is used in order to extend the life of the finishing tool. Next, the blank is affixed by wax to a pedestal and the pedestal is secured to mounting equipment of the lathe and the second face of the blank is both rough lathed and finish lathed.
Various types of lathes are used by optical labs, and thus the shape of the pedestal may vary from lab to lab. For example, some optical labs have lathes with collets adapted to grip an outer, cylindrical surface of a pedestal. Other labs have lathes with a mounting pin having a zero Morse taper which is shortened from two inches to one inch and which is adapted to fit within a complemental, tapered recess of a pedestal.
It has also been proposed to make relatively thick lens blanks in one-piece, cup-shaped molds having a base which is adapted to be mounted on a holding jig of a lathe. In this manner, the blank need not be re-mounted on a pedestal. Recently, there has been increased interest in the use of cup-shaped molds for making lens blanks, since the bottom of the cup-shaped recess may have particular dimensions and contour in order to mold one side of the blank into a particular configuration, and thus only the remaining side of the blank need be lathed by the optical lab. Such molds reduce lathing time (particularly when the molding materials are difficult to lathe) and are especially useful for making multi-focal, toric, aspheric and other lens having posterior surfaces that are difficult to replicate. Conventionally, a rough lathing tool is used to remove the bulk of the blank material as well as the sides of the cup-shaped mold before a finish lathing tool is used on the remaining side of the blank.
In recent years, improved compositions for ocular lens molding materials have been developed (such as the compositions described in U.S. Pat. No. 4,818,801) but often are very expensive relative to conventional materials. It would be advantageous to make lens blanks as thin as feasible when using such improved compositions, in order to reduce the costs of the blank and also lower internal stresses in the molded and finished lens. However, thin lens blanks are more difficult to handle and mount than the thicker, typical lens blanks when using the conventional methods described above. Moreover, the rough lathing step used in conventional methods is somewhat time-consuming.